Thursday, February 18, 2016

Cryptosporidiosis
(is also called Crypto) is a diarrheal disease mainly caused by an obligate
intracellular protozoan parasite, Cryptosporidium
parvum, in which the parasite cannot complete its life cycle and reproduce
in the absence of a suitable host. C.
parvum acquired an ability to infect the intestinal epithelial cells in
gastrointestinal (GI) tract of the hosts and then undergo both asexual and sexual
cycles for their replications. According to the Center for Disease Control and
Prevention (CDC) report, Crypto is one of the most common waterborne diseases
in the United States. Between 2001 to 2010, Crypto was the leading cause of
waterborne disease outbursts, which linked to recreational water in the United
States (1). Most of the Crypto can be spread by drinking recreational water
contaminated with Crypto, eating raw food, exposure to stool from an infected
person or animal, but it is not spread through a contact with blood. Due to C. parvum high tolerance to chlorine,
they can survive in chlorinated environment for a long period of time, and this
is why people swallowing recreational water (such as water in swimming pool)
have higher risks to get Crypto infection.

Cryptosporidium parvum is one of several
protozoan parasite that cause Crypto in both animals and humans. It has a
monoxenous life cycle that is mainly stay in the GI tract of a single host.
Also, C parvum lacks of host and
organ specificity, ability for autoinfection, and resistance to antimicrobial (2),
which result in many aspects of the nature and pathogenic mechanisms of C. parvum remains unclear due to its
characteristics.

For the Cryptosporidium life cycle, it has both
asexual and sexual cycles to allow themselves to divide and replicate in host
epithelial cells. The life cycle begins with ingestion of sporulated oocysts
from the host, and excystation (emerge from a cyst) occurs once the oocysts
enter to the GI tract, and they will release four sporozoites which will
parasitize epithelial cells in GI tract (Figure 1). Within these infected
epithelial cells, C. parvum can
undergo two additional asexual replication and release merozoites, which then
they will undergo sexual cycle and produce microgametes (male) and macrogametes
(female), which give arise to the zygote (fusion of both male and female
gametes) and form oocysts (Figure 1). Then the cycle repeats from the ingestion
of oocysts from the hosts.

The
pathogenesis of Cryptosporidium in
which causing diarrhea is still poorly understand. The suggested mechanism may
be involving a host-parasite interaction in which the attachment of C. parvum surface protein on the host
surface cell is the initial step for Crypto to occur. One of the C. parvum surface protein has been
identified that plays a role in mediating attachment and invasion on intestinal
epithelial cells of the hosts (3). It is believed that C. parvum surface protein acts like a ligand that binds to a
receptor on the surface of the host epithelial cell and initiates attachment
and invasion process to allow oocysts enter the GI tract and begins cell
divisions.

Cryptosporidial
infection can be transmitted from contaminated food and water, from animal to
person contact, and via person to person contact. The infection mainly infects
children due to their incomplete development of immune system. The major
transmission pathway for cryptosporidial infection is going through the
fecal-oral route from infected hosts directly or indirectly via contaminated
water or ingestion of contaminated food. Crypto is one of the frequent cause of
waterborne diarrhea because small infectious dose is enough to cause infection.
Also, due to their oocysts’ high resistance to disinfectants and other
chemicals used in recreational and drinking water, Cryptosporidium has emerged frequently in most of the waterborne
diseases in the United States. In fact, the source for Crypto mainly comes from
wild animals such as bovines, dogs, or cats that ingested C. parvum oocysts in the intestines. Once the humans accidently
make a contact with the stools of infected animals or humans, including
swallowing unsterilized water or eating uncooked food contaminated with Crypto.
In addition, individuals with immunodeficiency (failure of the immune system)
also have high risks for Crypto, such as the patients with AIDS (acquired
immunodeficiency syndrome) or cancer.

The
major diagnosis of Crypto is going through an examination of stool samples from
the patients or animals. Because of the detection of Crypto can be challenged,
several techniques have developed to identify Cryptosporidium such as acid-fast staining, is one of the reliable
and traditional method to detect the presence of cryptosporidial oocysts. Also,
in a view of immunology, using enzyme-linked immunosorbent assay (ELISA) and
antibody immunofluorescence assay (IFA) are the two alternative methods that
using antibodies to detect Cryptosporidium.
Both methods are used to detect protein-protein binding interaction between C. parvum surface protein and the host
cell surface protein, which allows healthcare providers to identify the
infection more efficient.

From a
genetic view of C. parvum infection,
a complete genome of C. parvum has
been recently identified (Abrahamsen, 2004). Several novel proteins of C. parvum cell surface and secreted
proteins have been identified, and it is believed these proteins have crucial
roles in host interaction and pathogenesis (4). In addition, targeting Cryptosporidium metabolic pathway or
enzymes may also have potentials for drug development (5). Still, due to lack
of sufficient information about C. parvum
pathogenesis, more genetic analysis are required to identify what genes or
proteins have contributions in attachment and invasion processes, and the virulence
of Crypto.

C. parvum is one
of the parasite that cause waterborne diseases in humans, and the health
problem have become a major concern in the United States. Because of C. parvum oocyst’s high resistance to
common disinfectants, sterilizing of recreational and drinking water still
becomes a challenge work today. Accurate detection with Cryptosporidial infections
is also a major challenge to healthcare providers, and more research is needed to
focus on pathogenesis of Crypto and development of drugs or therapies against C. parvum infection. Knowing mechanisms
and transmission of C. parvum
infection would allow researchers to be able to target the interaction between C. parvum surface protein and host cell
surface protein, which will prevent the first crucial step of Cryptosporidial
infection, attachment and invasion process. Therefore, a combination of both genetic
and pathological analyses are the essential approaches to treat Crypto in
future.

The most terrifying creature lurking below the
water’s surface does not have fins or razor sharp teeth. In fact, you can’t see it at all. The
microscopic amoeba, Naegleria fowleri, is
best known for its grotesque ability to digest and consume its victim’s brain. This ‘brain-eating’ amoeba may sound like Eli
Roth’s latest stomach-turning horror flick, but it’s no work of fiction and
it’s in the water. Each year, this
amoeba kills more people than sharks do in the United States1.
The single-celled organism can cause the deadly brain infection called
primary amebic meningoencephalitis (PAM), a disease that is nearly always fatal2.
Here is what you should know about the deadly infection and the current
research desperately seeking to find a treatment.

Infection occurs when a rush of contaminated water
enters the nose and the amoeba moves up the nasal cavity and into the brain3.
These tiny organisms swim by twitching fingerlike extensions called,
pseudopods2.
Once inside the brain, the parasite begins releasing proteins that cause
nerve and red blood cells to lyse, or break open, spilling the cell’s innards
for the organism to devour2.
The parasite can also use ‘sucking structures,’ known as ‘food-cups,’
located on the outside of the organism to rip open cells and feed on the
brain’s grey-matter4.
This process is shown in the figure below which was captured using a
scanning electron microscope capable of viewing these microscopic
organisms. The amoeba can be seen
tearing apart and devouring a cell5.
Destruction of these cells leads to severe swelling and necrosis, or tissue
death, resulting in devastating damage to the brain and often brain
hemorrhaging6.
Symptoms of the PAM progress quickly, often involving fever, nausea,
seizures, severe frontal headaches, and vomiting6.
Death generally occurs within 7-10 days of infection6.

While uncommon, the disease is virtually always
fatal6.Between 0 and 8 infections are reported every year in the United States7.Only three people have ever survived6.This is in part due to the difficulty detecting and treating the
infection6.Early symptoms often resemble the flu or other viral illnesses resulting
in misdiagnosis for 74% of initial healthcare visits during the beginning
stages of the disease6.As the disease progresses, incorrect diagnosis of bacterial meningitis
results because the symptoms are nearly identical consequently leading to 94%
of patients of patients receiving inappropriate treatment prior to diagnosis
with PAM6.Diagnosing PAM requires visually examining cerebrospinal fluid for
motile amoebas6.For timely identification, it is important for doctors to ask about
possible risk of exposure, such as recent freshwater swimming, in order to
begin treatment as early as possible6.

Exposure to the amoeba typically occurs while
swimming, diving, or during other water-related activities8.The amoeba is present in freshwater sources including lakes, rivers, and
untreated swimming pools8. Public health authorities are
encouraged to regularly monitor recreational waters at risk of contamination
and post appropriate warnings where high amounts of the amoeba have been
identified9.Proper chlorination of public pools can eliminate risk of infection9. Despite these attempts, infections
do still occur and the only known way to prevent infection is by avoiding nasal
contact with untreated fresh water7.

Despite the low risk of an infection with the
amoeba, water monitoring programs have shown that the organism is
wide-spread.A study examining water
sources in Arizona found the amoeba present in 17 out of the 19 samples
collected10.The question many experts have asked, is why then, do infections seem to
be so rare? “Almost every single person has antibodies in their blood which
indicate they were exposed at some point in time to the amoeba, but they didn’t
die from it,” said expert, Dr. Francine Marciano-Cabral, a professor of
microbiology and immunology at Virginia Commonwealth University who has studied
N. fowleri for more than 30 years11.She explains it could be that infection requires an encounter with a
large number of amoebas all at one time or, there may be a particular
subspecies which causes infection in humans while other subspecies are
nonthreatening11.Nearly all cases in the United States had occurred in southern states
(see map below), but recent expansion has brought the disease northward12.

In August 2010, the first confirmed case of PAM
in a northern state occurred in Minnesota and it was associated with local
freshwater exposure6,12.Since then, three additional cases have been reported in the Midwest
necessitating better awareness among providers across the US6,12.The amoeba is thermophilic meaning it thrives and rapidly multiplies in
warm temperatures9.The projected increase in temperatures due to global temperature change
could result in the infection being introduced to more areas that were previously
unaffected9.Recently, the number of infections reported annually appear to be rising
which could be a cause for concern6,13.While this may be due to improvements in surveillance, it is believed
that cases are still largely underreported6. Whether the increasing temperature
will lead to an increase in infections remains to be seen.Overall, the increase of infections,
expansion of the amoeba’s geographical range, and high fatality associated with
the disease makes finding an effective treatment for the infection more pressing.

One area of current research, aimed at finding a
treatment for the disease, involves understanding the amoeba’s ‘brain-eating’
abilities.How the amoeba destroys brain
tissue is not fully known.Studies,
focused on the potential causes for these deadly effects, suggest proteins
released by the amoeba may be involved.Dr. Kenneth Aldape believes cysteine proteases may be contributing to
the tissue destruction caused by the amoeba14.Cysteine proteases are enzymes that work by cutting up proteins into
pieces9.This damage can eventually result in the
death of the cell14.These conclusions were based on experiments where an irreversible
cysteine protease inhibitor was applied to the amoeba14.The inhibitor inactivates the amoeba’s enzyme preventing it working
properly.When the inhibitor was added
to the amoeba? They were no longer able to kill cells14.These results suggest that these specific enzymes are required in order
for the amoeba to kill cells during infection14.While non-disease causing amoeba produce similar proteases, the ability
to function at human body temperature is unique to this particular species15.

One specific set of
these cysteine proteases investigators are focusing on is, naegleriapores,
which poke holes into the cell-membrane exposing the cell’s interior16.Two of these proteins, named naegleriapore A and B, were discovered by
Dr. Rosa Herbst at the Bernhard Nocht Institute for Tropical Medicine in
Germany16.The studies by Dr. Herbst identified these proteins by measuring their
ability to pierce the cell-membrane16.Examining the structure of these proteins unveiled that they were
actually fragments of the same, larger protein16,17.A process leading to a large arsenal of protein forms capable of
destroying cells16,17.

The identification of
these proteins is an important step towards understanding this deadly
disease.Scientists are hopeful that one
of these proteins may lead to a treatment.Until then, education for rapid diagnosis and treatment are
essential.

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